"if you think childlike, you'll stay young. If you keep your energy going, and do everything with a little flair, you're gunna stay young. But most people do things without energy, and they atrophy their mind as well as their body. you have to think young, you have to laugh a lot, and you have to have good feelings for everyone in the world, because if you don't, it's going to come inside, your own poison, and it's over" Jerry Lewis
"I don’t believe
in the irreversibility of situations" Deleuze

Note on Citations

The numerical citations refer to page number. The source's text-space (including footnote region) is divided into four equal portions, a, b, c, d. If the citation is found in one such section, then for example it would be cited p.15c. If the cited text lies at a boundary, then it would be for example p.16cd. If it spans from one section to another, it is rendered either for example p.15a.d or p.15a-d. If it goes from a 'd' section and/or arrives at an 'a' section, the letters are omitted: p.15-16.

[The following is summary, up to the end where I reproduce this section in full. My commentary is in brackets.]

David Hume

A Treatise of Human Nature

Book I: Of the Understanding

Part II: Of the Ideas of Space and Time

Section VI: Of the Idea of Existence, and of External Existence

§152

We previously explained our mistaken ideas about space and time. We have similar problems with the ideas of existence and external existence. So we will contend with them now. By doing so, we will be better prepared for the next chapter on knowledge and probability.

§153

We possess many various impressions and ideas in our mind and memory. Yet we conceive none of them as non-existent.

from this consciousness the most perfect idea and assurance of being is derived. (66b)

So, we never remember any idea or impression without thereby conceiving it as existing. And also, we have the distinct idea of existence itself. There are two possibilities then:

1) the idea of existence is a conjoined part of every perception or conceptual object. Then, we derive the idea of existence from these perceptions and objects. Or,

2) the idea of existence remains one with the idea of the conceptual object or perception, and we never extract an additional separate idea of existence itself.

§154

We noted before the basic principle that every idea arises from a similar impression. Yet, no two distinct impressions can be inseparable, if truly they are distinct. So it cannot be that any impression has the idea of existence as a separable part.

And thus, tho' every impression and idea we remember be consider'd as existent, the idea of existence is not deriv'd from any particular impression. (66d)

§155

So the idea of existence cannot be separate from any idea of an existing thing. That is to say,

The idea of existence, then, is the very same with the idea of what we conceive to be existent. To reflect on any thing simply, and to reflect on it as existent, are nothing different from each other. (66-67)

We may only conceive ideas as existing. So the idea of existence does not add anything to conceptual objects.

Any idea we please to form is the idea of a being; and the idea of a being is any idea we please to form. (67a)

§156

Those who might disagree with Hume would argue that every perception or thought is conjoined to an impression which gives us the idea of existence. To defend his position, Hume dares his opponents to

1) exhibit that impression which is the source for our idea of 'entity,' and

2) prove that every perception we have also is conjoined with this impression.

But we know already that even though we have contemporaneous sensations, we still may always distinguish one from the other. So no one could possible show that this impression is conjoined to any perception, let alone every perception. [So we never really have a perception of a tree, for example, from which we obtain two impressions: a) an impression of a tree, and b) another impression of an existing entity. Rather, we have just one impression: the impression of an existing tree. But it is redundant even to refer to the tree as existing, because we cannot conceive it any other way.]

§157

Recall Hume's white globe example in §61. We saw a white globe. We were not able to conceive the white without the spherical shape, nor could we conceive the spherical shape without the white color. However, we were able to make a "distinction of reason" when we associated the white globe with other white things and with other spherical things. Hume says now that this sort of distinction of reason will not apply to the case of the idea of a thing's existence. All objects presented to us resemble each other insofar as they are all existing objects. We encounter no non-existing objects, so we cannot make such a distinction of reason between the two.

§158

Hume will use similar reasoning to show that we also do not have a separate idea of 'external existence.' It is clear that the only things that are present to the mind are its perceptions, impressions, and ideas. We know also that we come to know external objects by these means only. Now consider that we sometimes hate external objects. We also love them. And we think about them. As well do we feel and see them. So all these actions are no more than perceptions.

§159

So, only perceptions are present to the mind. And, all ideas are derived from things that were just previously present to the mind. Now, because all our ideas derive from what is present in the mind, and because only impressions are present to the mind, then we cannot form ideas of things that are specifically different from their impressions. Hume invites us to think about things as far beyond us as possible, so that we may see we never leave our imaginations in doing so.

Let us chase our imagination to the heavens, or to the utmost limits of the universe; we never really advance a step beyond ourselves, nor can conceive any kind of existence, but those perceptions, which have appeared in that narrow compass. This is the universe of the imagination, nor have we any idea but what is there produced. (67-68)

§160

So we are unable really to conceive of objects in their externality. However, later Hume will show that we may in the very least form a relative idea of external objects, by attributing certain relations, connexions, and durations to our ideas.

Sect. vi. Of the Idea of Existence, and of External Existence.

It may not be amiss, before we leave this subject, to explain the ideas of existence and of external existence; which have their difficulties, as well as the ideas of space and time. By this means we shall be the better prepared for the examination of knowledge and probability, when we understand perfectly all those particular ideas, which may enter into our reasoning.

There is no impression nor idea of any kind, of which we have any consciousness or memory, that is not conceived as existent; and it is evident, that from this consciousness the most perfect idea and assurance of being is derived. From hence we may form a dilemma, the most clear and conclusive that can be imagined, viz. that since we never remember any idea or impression without attributing existence to it, the idea of existence must either be derived from a distinct impression, conjoined with every perception or object of our thought, or must be the very same with the idea of the perception or object.

As this dilemma is an evident consequence of the principle, that every idea arises from a similar impression, so our decision betwixt the propositions of the dilemma is no more doubtful. So far from there being any distinct impression, attending every impression and every idea, that I do not think there are any two distinct impressions, which are inseparably conjoined. Though certain sensations may at one time be united, we quickly find they admit of a separation, and may be presented apart. And thus, though every impression and idea we remember be considered as existent, the idea of existence is not derived from any particular impression.

The idea of existence, then, is the very same with the idea of what we conceive to be existent. To reflect on any thing simply, and to reflect on it as existent, are nothing different from each other. That idea, when conjoined with the idea of any object, makes no addition to it. Whatever we conceive, we conceive to be existent. Any idea we please to form is the idea of a being; and the idea of a being is any idea we please to form.

Whoever opposes this, must necessarily point out that distinct impression, from which the idea of entity is derived, and must prove, that this impression is inseparable from every perception we believe to be existent. This we may without hesitation conclude to be impossible.

Our foregoing reasoning [Part I. Sect. 7.] concerning the distinction of ideas without any real difference will not here serve us in any stead. That kind of distinction is founded on the different resemblances, which the same simple idea may have to several different ideas. But no object can be presented resembling some object with respect to its existence, and different from others in the same particular; since every object, that is presented, must necessarily be existent.

A like reasoning will account for the idea of external existence. We may observe, that it is universally allowed by philosophers, and is besides pretty obvious of itself, that nothing is ever really present with the mind but its perceptions or impressions and ideas, and that external objects become known to us only by those perceptions they occasion. To hate, to love, to think, to feel, to see; all this is nothing but to perceive.

Now since nothing is ever present to the mind but perceptions, and since all ideas are derived from something antecedently present to the mind; it follows, that it is impossible for us so much as to conceive or form an idea of any thing specifically different from ideas and impressions. Let us fix our attention out of ourselves as much as possible: Let us chase our imagination to the heavens, or to the utmost limits of the universe; we never really advance a step beyond ourselves, nor can conceive any kind of existence, but those perceptions, which have appeared in that narrow compass. This is the universe of the imagination, nor have we any idea but what is there produced.

The farthest we can go towards a conception of external objects, when supposed SPECIFICALLY different from our perceptions, is to form a relative idea of them, without pretending to comprehend the related objects. Generally speaking we do not suppose them specifically different; but only attribute to them different relations, connections and durations. But of this more fully hereafter.[Part IV, Sect. 2.]